Helmet-shaped aquarium



FIG. 1 is a perspective view of a helmet-shaped aquarium, showing the new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a left-side elevational view thereof; right-side elevational view being a mirror image thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof. 

What is claimed is the ornamental design for a helmet-shaped aquarium, as shown and described. 